Catheters including balloons are routinely used to resolve or address flow restrictions or perhaps even complete blockages in tubular areas of a body, such as arteries or veins. In many clinical situations, the restrictions are caused by hard solids, such as calcified plaque, and may sometimes involve the use of high pressures to compact such blockages. Commercially available balloons employ complex technology to achieve high pressure requirements without sacrificing the profile of the balloon. Besides high pressure requirements, the balloons should also be resistant to puncture, easy to track and push, and present a low profile, especially when used for angioplasty.
The clinician performing the angioplasty procedure should be able to locate the position of the uninflated balloon with accuracy, so that the balloon will be properly positioned once inflated. This is conventionally accomplished by attaching marker bands on the catheter shaft corresponding to the ends of the balloon working surface. This “working surface” is the surface along the portion of the balloon that is used to achieve the desired treatment effect, such as contacting the calcified plaque (which surface in the case of a balloon having conical or tapering sections at the proximal and distal ends is typically co-extensive with a generally cylindrical barrel section).
However, misalignment of the marker bands during placement along the shaft sometimes results in their failure to correspond precisely to the extent of the working surface. This misalignment may prevent the clinician from accurately identifying the location of the working surface of the balloon during an interventional procedure. Also, when successive intravascular interventions are made, such as during a pre-dilatation using a first catheter followed by dilatation using a second catheter, the clinician must guess at the location where the pre-dilatation occurred. In either case, this uncertainty may lead to a geographic misalignment, or “miss,” of the desired contact between the intended treatment area and the working surface of the balloon. It is especially desirable to avoid such an outcome when the balloon is designed to deliver a payload (such as a therapeutic agent (e.g., a drug, such as paclitaxel, rapamycin, heparin and the like), a stent, a stent graft, or a combination thereof) or a working element (such as a cutter, focused force wire, or the like) to a specified location within the vasculature, since a miss may, at a minimum, prolong the procedure (such as, for example, by requiring redeployment of the balloon or the use of another balloon catheter in the case of a drug coated balloon), and possibly result in an inferior outcome if the lesion is not properly treated as a result of the misalignment.
In order to assess the length of a lesion from a location external to the body, a clinician may use an external ruler, which in one form is called a “LeMaitre” tape. While the use of such a ruler or tape may allow for a more precise assessment of the lesion length and an area treated by a pre-dilitation step, it is not without limitations. For one, a displacement or difference in the apparent position of the lesion margins results when viewed along two different lines of sight. This “parallax” can lead to an inaccurate measurement and, at a minimum, contribute to the geographic misalignment of the working surface relative to the lesion. The use of such a ruler may also lead to inferior measurements when the vasculature at issue is particularly tortuous.
Accordingly, a need exists for a manner in which to position a balloon catheter into the vasculature at a treatment area with enhanced accuracy, and also in a manner that is highly repeatable.